High-frequency periodic deformation of polymers in the viscous-flow state

The propagation of high-frequency periodic vibrations in melts and solutions is considered in the case where the acoustic characteristics of the material are determined by the deformation amplitude. It is shown that in sufficiently large specimens the consequences of periodic deformation are concentrated near the vibration source, as a result of which a layer of material with strongly modified mechanical characteristics develops. It is suggested that when periodic high-frequency deformation is superimposed on steady-state flow, owing to the presence of a boundary layer there is effective slippages of the material at the vibration-emitting surfaces.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 4, pp. 722–728, July–August, 1973.     

Nature of the friction deformation of the surface layers of polymethyl methacrylate

The surface deformation of amorphous thermoplastics (polymethyl methacrylate) by a spherical steel indentor has been investigated at various sliding velocities. Small velocities correspond to elastic and forced-elastic deformation of the surface layers and asperities. At temperatures corresponding to the high-elastic state the deformed surface layer completely recovers its shape. As the sliding velocity increases, the forced-elastic deformation is localized in a thinner layer of plastic. Starting from a certain velocity, depending on the temperature and the activation energy for transition of the chain segments from one equilibrium position to another in the process of thermal motion, the deformation of the surface layers and asperities becomes purely elastic. In the event of elastic deformation at pressures above a certain value the surface layer of plastic suffers brittle fracture in the tensile zone behind the indentor.Mekhanika Polimerov, Vol. 4, No. 1, pp. 90–94, 1968.     

Electron-fractographic investigation of the brittle fracture of polyethylene

The results are presented of an electron-microscope investigation of the brittle fracture of linear polyethylene at the temperature of liquid nitrogen. It is shown that the physical nature of the structural details of the microrelief of the fracture surface is conditioned by local plastic deformation of the stratified lamellar structures in a thin layer adjacent to the fracture surface preceding and accompanying fracture. The possibility of local self-heating is discussed and a possible mechanism of plastic deformation of the crystal platelets at low temperatures is proposed.Mekhanika Polimerov, Vol. 3, No. 2, pp. 286–290, 1967     

Deformation of composite materials based on modified thermally expanded graphite

Samples of thermally expanded graphite modified with aluminosilicates of varying concentration and undergoing bulk tests in conditions of uniaxial compression were investigated. Micromechanical tests were performed on the surface of the samples by the method of continuous indentation with an indenter. The deformation of the surface layer and bulk of the samples was investigated. It was found that the compressive strength of the samples of modified thermally expanded graphite increased with an increase in the degree of deformation. Modification of the thermally expanded graphite powder with aluminum compounds allows fabricating articles with deformation strength.Institute of Surface Chemistry, National Academy of Sciences of Ukraine. Kiev. Translated from Mekhanika Kompozitnykh Materialov, Vol. 33, No. 4, pp. 443–449, July–August, 1997.     

Prediction of changes in the strength of filled thermoplastics upon aging in an oxidizing atmosphere

Problems related to analyzing specimens with damaged surface layers have been examined using polyamide, trioxane—dioxolane copolymer, and polycarbonate as source materials. A model was developed for the brittle fracture of block specimens with damaged surface layers, which provides an estimate of the restraints to plastic deformation in these layers. Three segments are seen in the strength—time curves featuring 1) increasing strength, 2) decreased strength with brittle fracture, and 3) constant low strength. The strength of filled specimens of a specific period permits us to evaluate the effect of the filler on the fracture resistance of the matrix. A method was proposed for predicting the strength of filled samples using the matrix aging data.Translated from Mekhanika Kompozitnykh Materialov, Vol. 29, No. 3, pp. 375–380, May–June, 1993.     

Morphology of fractured polymer surfaces self-bonded below the glass transition temperature

Previosly noncontact surfaces of polystyrene (PS) and poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) were self-bonded in a lap shear joint geometry below the glass transition temperature T_g The joints were then fractured in tension at room temperature and the contact area was analyzed by means of scanning electron microscopy. Zones of plastic deformation were revealed on the surfaces of PS and PPO which had been bonded at T_g–33 and T_g–70°C, respectively, thus indicating interdiffusion across the interface. This result points to the lower T_g of the surface layer as compared with that of the bulk sample, in agreement with our previous studies. The unusually high self-bonding ability of PPO (at very low temperatures related to the bulk T_g) is presumably due to the low depth of penetration required to establish entanglements.Presented at the 10th International Conference on the Mechanics of Composite Materials (Riga, April 20–23, 1998).Published in Mekhanika Kompozitnykh Materialov, Vol. 34, No. 5, pp. 665–672, September–October, 1998.     

Breakdown of high-pressure polyethylene in bulk

The mechanism of polyethylene breakdown in bulk at low initial stresses, relaxing during the breakdown process, is discussed. Optical, electron, and scanning microscopy were used to investigate the surface of disintegrating polyethylene for cable insulation. It was found that in prolonged tests the breakdown surface has an appearance typical for the brittle breakdown of glass polymers. It was also established that in the case of brittle breakdown with clearly expressed mirror-like and rough zones, the disintegration process passess passes through an evident deformation of the surface layer and the formation of micronecks prior to rupture.Translated from Mekhanika Polimerov, No. 5, pp. 935–936, September–October, 1972.     

Dynamic method of determining the mechanical characteristics of the surface layer of polymers

A thin polymer film is treated as a three-layered plate, the inner layer being characterized by the bulk and the outer layers by the surface properties of the polymer. Using the equations describing the vibrations of a cantilever element of rectangular section, the authors propose formulas for the thickness, modulus of elasticity, and mechanical loss factor of the surface layer. The mechanical characteristics of the surface layers of PMM and nitrocellulose have been determined by electromagnetically exciting and photometrically recording vibrations in film specimens of varying thickness.Institute of the Chemistry of High-Molecular Compounds, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Mekhanika Polimerov, No. 3, pp. 548–550, May–June, 1969.     

Thermomechanical properties of spot-bonded nonwoven synthetic-fiber materials

The thermomechanical properties of spot-bonded nonwoven synthetic-fiber materials with a polymer binder have been investigated. The materials are composed of heterogeneous fibers, with low-melting polymers (binder) forming the surface layer. The change of deformation in uniaxial tension was studied from 20 to 150° C (rate of temperature increase 1.5° C/min) as a function of the nature of the fibers and the binder, their relative proportions, and the density and weight of the material. A theoretical explanation of the observed effects is offered.Mekhanika Polimerov, Vol. 4, No. 2, pp. 300–303, 1968     

Equilibrium shear of rubber specimens in practical testing

The stress and strain distribution in rectangular rubber specimens in equilibrium shear has been analyzed with allowance for the effect of the inhomogeneity of large nonlinear deformations. The results obtained satisfy the basic equations of the nonlinear theory of elasticity as well as the experimental data on the displacements of the points of a rectangular grid inscribed on the surface of the specimens before deformation.Mekhanika Polimerov, Vol. 3, No. 6, pp. 1024–1029, 1967     

Equilibrium compression of rubber samples in practical tests

The distribution of stresses and strains in equilibrium uniaxial compression of cylindrical and rectangular rubber specimens is analyzed with consideration for the effect of friction forces on the ends and of the nonlinearity of the relation between stresses and strains. The results obtained satisfy the basic equations of the nonlinear theory of elasticity and experimental data on the displacements of points of a rectangular grid applied to the surface of underformed specimens due to deformation.Mekhanika Polimerov, Vol. 1, No. 4, pp. 81–88, 1965     

Friction of polymeric materials

The case of contact of polymer and metallic surface has been examined. A formula is proposed for calculating the contact area as a function of time of holding the compression surface under load and for calculating the coefficient of friction, the dependence of Young's modulus and shear strength on temperature, deformation rate, and average force on the contact surface being taken into account. The nature of deformation of irregularities on the surfaces of polymeric materials under the action of normal and tangential loading has been examined.See [1] for Communication 1.Institute for Polymer Mechanics, Academy of Sciences of the Latvian SSSR, Riga. Translated from Mekhanika Polimerov, No. 5, pp. 809–815, September–October, 1972.     

Effect of the size of the specimen cross section on the long-term strength of polyethylene

The scale effect has been investigated in relation to the long-term strength of specimens of high-density polyethylene. Time dependences of the tensile strength at ordinary temperatures have been obtained. It is shown that the long-term strength depends on the dimensions of the specimen cross section. The deformation of the specimens depends on their size and the shape of the gage cross section.Higher Chemical Technology Institute, Sofia. Translated from Mekhanika Polimerov, No. 4, pp. 741–743, July–August, 1973.     

Adhesion of polyethylene in simultaneous deformation

The strength of the joints arising as a result of the mutual deformation of polyethylene specimens is studied, and it is shown that mutual deformation can lead to the formation of a strong joint.Mekhanika Polimerov, Vol. 2, No. 4, 574–579, 1966     

Study of the prefracture states of rigid polymers 1. Forced high-elastic deformation

It is shown that in the process of extension specimens of a rigid unoriented polymer — polyethylene terephthalate — go over into the oriented state before failure. Various cases of transition to the oriented state are considered: with the formation of a neck and deformation bands, with and without loss of continuity. The degree of molecular orientation of the specimens and their fracture conditions are estimated.A. F. Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 8–14, January–February, 1976.     

Kinetics of formation of the actual contact area in rubbery materials

The kinetics of formation of the actual contact area in rubbery materials is investigated. A procedure for determining the relaxation spectrum of the segmental motion of the macromolecules in the surface layer of a polymer in contact with a solid surface is proposed. The effect of temperature and the applied specific load on H() is determined. The activation energy of segmental motion of the macromolecules in a thin surface layer of the specimen is calculated.Second Moscow Pirogov State Medical Institute. Translated from Mekhanika Polimerov, No. 6, pp. 1047–1052, November–December, 1971.     

Effect of liquid media on the deformation of the surface layers of a polymer-metal pair in sliding friction

The relation between the high-elastic component of polyurethane deformation and the deformation of the surface layers of metals has been investigated for sliding friction in various media. The surface layers of polymer and metal are plastically deformed. There is a certain correlation between the coefficient of friction and the amount of deformation.Kiev Institute of Civil Aviation Engineers. Translated from Mekhanika Polimerov, No. 1, pp. 147–149, January–February, 1970.     

Experimental study of the contribution of interfacial friction to the deformation resistance of particle-reinforced polymers

A study has been made of the dissipative properties of heavily filled elastomers as influenced by friction of the elastic matrix on the surface of the solid filler particles. In order to model the frictional surface, specimens were predamaged by cyclic deformation, with strain amplitudes sufficient to cause separation of the matrix from the filler. The predeformation operation was performed by means of a mechanical system having individual particle-matrix bonds, so that it was possible to evaluate the contribution of interfacial friction to the resistance of the polymer. When external pressure was applied to the specimens, the width of the hysteresis loop increased with increasing pressure, obviously reflecting an increase of the surface friction in the matrix. It was established that for a given volumetric fill, the dissipation of mechanical energy increased with decreasing particle size (with increasing frictional surface area). The significant influence of interfacial friction on the level and rate of strain relaxation was demonstrated experimentally.Paper presented at the 9th International Conference on the Mechanics of Composite Materials (Riga, October 1995).Translated from Mekhanika Kompositnykh Materialov, Vol. 31, No. 5, pp. 579–583, September–October, 1995.     

Effect of loading rate on polymer wear

The effect of loading rate on polymer wear in metal-polymer friction pairs is considered. Investigations show that at low loading rates the wear resistance of the polymer specimens increases, evidently owing to orientation of the elements of the molecular structure in the surface layer. This finding applies both to dry friction and friction with lubricants.Mekhanika Polimerov, Vol. 2, No. 6, pp. 862–866, 1966     

Determination of mass entrainment of heat-insulating materials from the deformation of stressed casings

A method has been developed for the determination of mass entrainment and reinforcing layer boundaries of stressed casings subjected to erosion and thermal degradation. The method is based on the determination of the stresses acting on the casing and the measurement of casing deformation by means of tensometers (strain gages), installed on the external surface. Results obtained in the experimental verification of the method by model tests carried out on glass-plastic single and double-layer casings are presented.Deceased.P. I. Baranov Central Institute of Aeroengine Design, Moscow. Translated from Mekhanika Polimerov, No. 5, pp. 824–828, September–October, 1972.